1. Field of the Invention
This invention relates to an apparatus and method for recording information, such as Fresnel holograms, and in particular, to recording lensless digital incoherent Fresnel holograms using a mask, such as an absorption-only mask.
2. Discussion of the Background
Holograms recorded by incoherent light open many new applications like outdoor and astronomical holography (J. B. Breckinridge, “Two-Dimensional White Light Coherence Interferometer,” Appl. Opt. 13, 2760 (1974)) and fluorescence holographic microscopy (G. Indebetouw, A. El Maghnouji, R. Foster, “Scanning holographic microscopy with transverse resolution exceeding the Rayleigh limit and extended depth of focus,” J. Opt. Soc. Am. A 22, 892-898 (2005)). The oldest methods of recording incoherent holograms have made use of the property that every incoherent object is composed of many source points each of which is self spatial coherent and therefore can create an interference pattern with light coming from the point's mirrored image. Under this general principle there are various types of holograms (J. B. Breckinridge, “Two-Dimensional White Light Coherence Interferometer,” Appl. Opt. 13, 2760 (1974)) (A. W. Lohmann, “Wavefront Reconstruction for Incoherent Objects,” J. Opt. Soc. Am. 55, 1555-1556 (1965)) (G. Sirat, D. Psaltis, “Conoscopic holography,” Optics Letters, 10, 4-6 (1985)) including Fourier (J. B. Breckinridge, “Two-Dimensional White Light Coherence Interferometer,” Appl. Opt. 13, 2760 (1974)) (G. W. Stroke and R. C. Restrick, “Holography with Spatially Incoherent Light,” Appl. Phys. Lett. 7, 229 (1965)) and Fresnel holograms (G. Cochran, “New method of making Fresnel transforms,” J. Opt. Soc. Am. 56, 1513-1517 (1966)) (P. J. Peters, “Incoherent holography with mercury light source,” Appl. Phys. Lett. 8, 209-210 (1966)). The process of beam interfering demands high levels of light intensity, extreme stability of the optical setup and a relatively narrow bandwidth light source. These limitations have prevented holograms from becoming widely used for many practical applications.
More recently two groups of researchers have proposed to compute holograms of 3-D incoherently illuminated objects from a set of images taken from different points of view. (Y. Li, D. Abookasis and J. Rosen, “Computer-generated holograms of three-dimensional realistic objects recorded without wave interference,” Appl. Opt. 40, 2864-2870 (2001)) (Y. Sando, M. Itoh, and T. Yatagai, “Holographic three-dimensional display synthesized from three-dimensional Fourier spectra of real existing objects,” Opt. Lett 28, 2518-2520 (2003)) This method, although it shows promising prospects, is relatively slow since it is based on capturing tens of images of the subject scene from different view angles.
Another method is called scanning holography (G. Indebetouw, A. El Maghnouji, R. Foster, “Scanning holographic microscopy with transverse resolution exceeding the Rayleigh limit and extended depth of focus,” J. Opt. Soc. Am. A 22, 892-898 (2005)) (Poon T.-C., “Three-dimensional image processing and optical scanning holography,” Adv. in Imag. & Elec. Phys. 126, 329-350 (2003)) in which a Fresnel Zone Plate (FZP) pattern is scanned across the object such that at each and every scanning position the light intensity is integrated by a point detector. The overall process yields a Fresnel hologram obtained as a correlation between the object and FZP patterns. However the scanning process is a relatively slow and is done by mechanical movements. A similar correlation is actually done also in the present work; however, unlike the case of scanning holography, we propose here a correlation without movement.
Mertz and Young (L. Mertz and N. O. Young, “Fresnel transformations of images,” in Proceedings of Conference on Optical Instruments and Techniques, K. J. Habell, ed. (Chapman and Hall, London 1961) p. 305) already proposed holographic photography based on correlation without movement between object and FZPs. However, their process relies on geometrical optics, which cannot yield good imaging results in the optical regime. On the contrary, our suggested correlator for implementing the holographic recording is valid in the optical regime, since its operation principle is based on the diffraction theory (J. Goodman, Introduction to Fourier Optics, 2nd ed., McGraw-Hill, New York, 1996, pp. 63-95 (Chapter 4)).